The overall goal of the proposal outlined here is to study the structure to function relationship of cell-surface membrane components expressed on cytotoxic T lymphocytes (CTL). This objective is composed of three specific aims which will be approached in the following manner: I. Establishment and characterization of functionally distinct alloreactic T cell clones of defined antigenic specificity. These clones of both anti-Ia T "helper" cells and CTL will be selected for stable in vitro function and specificity against different regions of the sensitizing H-2 complex. II. Application of recently developed immunization techniques which will greatly favor the detection of less immunogenic, "CTL-specific" differentiation structures and "functionally-relevant" membrane determinants. III. "Capture" of antibody specificities raised by these immunizations using hybridoma technology. Monoclonal antibodies specifically reactive with CTL will then be used to investigate the functional role of these determinants as possible participants decisive for lytic function. Inhibitory effects of these monoclonal antibodies will be assay both at the level of recognition/binding function of CTL and in expression of effector mechanism. Monoclonal antibodies defining both CTL-specific and "killing relevant" membrane structure will be used to isolate these molecules for biochemical characterization. In addition, these antibodies will be used to examine their topographical display and physical associations on the cell surface. The results from this approach will further our understanding of how membrane determinants on CTL dictate and regulate immune reactivity.